neutral relay

A relay thus wound is known as a differential relay--more generally called a neutral relay.

The general principles of quadruplex telegraphy are based upon the phenomena which we have briefly outlined in connection with the neutral relay and the polar relay.

If, however, the transmitter is operated at the same end, the entire battery is connected to the main line, and the strength of this current is sufficient to operate the neutral relay.

If another battery, D, be introduced at the distant end of the wire A the differential or neutral relay becomes actively operative as follows: Battery C supplies wires A and B with an equal current, but battery D doubles the strength of the current traversing wire A.

Before finally dismissing the quadruplex, and for the benefit of the inquiring reader who may vainly puzzle over the intricacies of the circuits shown in Fig. 8, a hint as to an essential difference between the neutral relay, as used in the duplex and as used in the quadruplex, may be given.